I have a portfolio item with link to the post. When I navigate to that post there is no selected item in the menu (Portfolio should remain selected) and when I click on “Portfolio” to get back, I end up in “Home” with Home selected.

This happens in both Single and Multipage layouts, although I’m interested in the Single layout.

Ok – this seems to be a limitation by design. Kriesis “one-page” menu doesn’t use the standard wordpress menu classes which would allow you to style the current page item or the ancestor/parent of the current page/post/menu item. I’ll ask Kriesi to look into it – maybe he can work out a clever solution.